US 2002/0183191 discloses a three-way catalyst comprising a zeolite/alumina composite catalyst support exhibiting a modulus of rupture of at least 750 psi and having a zeolite with a silica/alumina ratio of at least 300, which catalyst support is impregnated with a noble metal selected from the group consisting of platinum, rhodium, iridium and palladium. The three-way catalyst has high cell density, thin walls and no washcoat. In one embodiment, the catalyst support contains optionally stabilised zirconia in addition to the zeolite and alumina. The zirconia dopant can include cerium oxide in amounts up to 80 wt % based on the total zirconium amount. However, no Example including optionally doped zirconia is provided.
US '191 explicitly excludes washcoating with a catalyst-containing slurry to avoid a reduction in the channel size of a honeycomb and increased backpressure. Furthermore, the use of silica binder is excluded because of incompatibility between silica and platinum group metals. Hence, gamma alumina is used as the binder. However, in the comparison examples provided, the three-way catalyst performance (measured as light off temperature for converting CO, NOx and hydrocarbons) of catalysts according to the invention, particularly for 50:50 and 40:60 weight ratios of zeolite:gamma alumina, compare poorly with comparative examples comprising an alumina-only extruded support or a zeolite/silica binder-based support.
U.S. Pat. No. 5,772,972 discloses an automotive catalyst system for treating internal combustion engine exhaust gases. The system comprises a hybrid system of a zeolite hydrocarbon trap and a palladium-based three-way catalyst material carried on a substrate monolith. In one embodiment, the three-way catalyst is layered on an extruded zeolite substrate monolith. However, no specific Example including an extruded zeolite substrate monolith is provided.
EP 1739066 discloses a honeycomb structure comprising multiple honeycomb units having multiple through holes; and a seal layer that joins honeycomb units with each other via respective closed outer faces of the honeycomb units where the through holes are not open. The honeycomb unit includes at least inorganic particles, inorganic fibers and/or whiskers. The inorganic particles exemplified are alumina, titania, silica and zirconia; the inorganic fibres exemplified are silica alumina fibres; and the inorganic binders exemplified are silica sol, alumina sol, sepiolite and attapulgite. A catalyst component can be carried on the honeycomb structure. The catalyst component may include at least one type selected among noble metals including platinum, palladium and rhodium, alkali metals such as potassium and sodium, alkaline earth metal e.g., barium and oxides. The honeycomb structure can be used as a catalytic converter e.g., a three-way catalyst or a NOx storage catalyst for conversion of the exhaust gas of vehicles.